The present invention relates to a device for the controlled release of an active agent to a host. In particular, the present invention relates to a transdermal delivery patch having a monolithic polymeric carrier layer into which the active agent is melt-blended. More particularly, the present invention relates to transdermal devices for the topical application of active agents such as nicotine.
Transdermal administration systems are well-known in the art. Occlusive transdermal patches for the administration of an active agent to the skin or mucosa are described in U.S. Pat. Nos. 4,573,996, 4,597,961 and 4,839,174.
One type of transdermal patch is a polymer matrix or monolithic device in which the active agent is dissolved or suspended in a polymer matrix film through which the active agent diffuses to the skin. Such patches are preferred because they are relatively simpler to manufacture compared to reservoir-type devices. Transdermal patches having a monolithic polymer film layer into which the active agent is dissolved or suspended are disclosed by the above-mentioned U.S. Pat. No. 4,839,174, as well as by U.S. Pat. Nos. 4,908,213 and 4,943,435.
U.S. Pat. Nos. 4,839,174 and 4,943,435 disclose that the active agent is incorporated into the monolithic polymer film layer by dissolving the active agent and the polymer into a common solvent, and then solvent-casting the film from the resulting solution. The solvent-casting of monolithic polymer film layers typically requires the evaporation of solvent from the cast film. This has proven to be problematic. Because the film is employed in skin contact end use applications, complete removal of the solvent is necessary. Solvent removal requires the application of elevated temperatures to the polymer film. The removal of solvent by heat-evaporation can strip the lower molecular weight components, including the active agent, from the film, even at temperatures below which these lower molecular weight components volatilize. Reducing the evaporation temperature to levels at which the lower molecular weight components are not stripped, substantially increases the amount of time required for evaporation and results in films having significant levels of residual solvent.
U.S. Pat. No. 4,840,796 discloses a transdermal drug delivery device having a monolithic polymer film layer into which the active agent is dissolved or suspended in which the polymer is a substantially linear block copolymer of a polydiorganosiloxane and a diisocyanate. The copolymer is reported as having a glass transition temperature between 45.degree. C. and 160.degree. C., making it possible to melt-blend the active agent with the copolymer by way of processes such as calendaring, extrusion, and the like. However, the processing of film layers from the disclosed melt-blends has proved problematic and, as disclosed at column 6, lines 5-11, solvent-casting of the melt-blends is still required in order to form polymer film layers containing an active agent for drug delivery.
A transdermal patch for the delivery of an active agent having a monolithic polymer film layer into which the active agent is dissolved or suspended without the use of solvents would be highly desirable.